Experimental study on shear response of alumina under combined compression and shear loading

The pressure-shear plate impact experiments and impact recovery experiments have been performed on 92.93% aluminas using 57 mm-diameter compressed-gas gun. And the inelastic behavior and shear wave propagation have been probed in polycrystalline ceramics under combined compression and shear loading. The compressed-gas gun drove the copper flyer to impact the oblique target parallelly, and the particle velocity is traced by embedded electromagnetic velocity gauge. The lateral particle velocities show an attenuation of shear waves with decreasing of material shear rigidity, which were decoupled from the histories of electromotive force induced by electromagnetic velocity gauges moving in magnetic field. Then SEM analysis of recovered samples shows the transit of intergranular microcracks to transgranular microcracks with increasing shock loading. Microcracks nucleate and expand along crystal boundaries and pores under loading of pressure-shear impact below the material yield threshold, and go further to transgranular microcracks with the loading above the yield threshold. The microcracks result in a remarkable dilation of alumina samples when unloaded.